Medical oxygen is normally provided to patients who require supplemental oxygen either from pressurized cylinders delivered to the patient's home or from an oxygen concentrator. An oxygen concentrator separates nitrogen from air to provide an oxygen enriched gas having a concentration of up to about 95% oxygen. The oxygen concentrator operates by using a compressor to apply pressurized air to a gas separation element, such as a molecular sieve bed, which will pass oxygen while having an affinity for nitrogen. Over a relatively short time, the gas separation element will become saturated with nitrogen and its efficiency decreases. Typically, an oxygen concentrator is provided with two or more molecular sieve beds. While at least one molecular sieve bed is operated to produce a flow of oxygen enriched gas, nitrogen is purged from at least one other molecular sieve beds by a limited back flow of the nitrogen free oxygen enriched gas from an operating sieve bed.
A common type of compressor used to operate an oxygen concentrator comprises a single electric motor having two reciprocating piston compressors driven from opposite ends of the motor shaft. Each compressor includes a piston which is reciprocated in a cylinder by the motor. The two cylinders are connected together to provide the air flow and pressure required to produce a desired maximum oxygen enriched gas output. An oxygen concentrator may be designed, for example, to provide a maximum continuous flow of 5 liters per minute, or more, of oxygen enriched gas having an oxygen concentration of up to about 95% at a pressure of 8.5 psig.
Oxygen enriched gas from an oxygen concentrator is delivered to the patient through a hose and a nasal cannula. The hose may be sufficiently long to allow the patient to walk around an area of his or her home. However, most oxygen concentrators are not sufficiently small and light weight to allow an ambulatory patient to leave the home. For trips away from the home, either a portable compressed oxygen cylinder or a portable liquid oxygen container are typically used to provide the patient's supplemental oxygen needs. Oxygen dealers deliver filled portable oxygen cylinders to the patient's home as needed by an ambulatory patient when traveling away from the home oxygen source. Regular home delivery of oxygen results on an ongoing high expense either for insurance companies or for the patient.
In addition to supplying oxygen enriched gas directly to a patient, some oxygen concentrators have been connected to a compressors or to a pressure intensifiers for increasing the gas pressure of the oxygen enriched gas product stream to the level needed for filling a portable cylinder which the patient may use when traveling away from the home. When the oxygen concentrator simultaneously provides the patient's requirements for supplemental oxygen and fills a cylinder, the time required to fill the cylinder is long, since the patient's needs must be met first and only oxygen enriched gas in excess of the patient's needs can be used to fill the cylinder. In some prior art cylinder filling oxygen concentrators, a separate stand alone motor driven compressor is used to increase the gas pressure to the level needed to fill the cylinder. In other cylinder filling oxygen concentrators, a portion of the above atmospheric pressure oxygen enriched gas from the oxygen concentrator has been used to drive a pressure intensifier which increases the pressure to the high level required to fill the cylinder.